This invention relates to methods for preparing polyheterosiloxanes with chemically bonded non-Si metal elements using both metal salts and metal alkoxides. The metal salts and metal alkoxides can contain the same or different metal elements. The polyheterosiloxanes prepared by these methods are solid materials which can be easily dispersed in a solvent of choice.
Incorporation of metal elements into polysiloxanes has been of great interest for a wide range of applications due to their ability to impart high refractive index, impact resistance, scratch resistance, fire retardance, anti-corrosion, anti-stain, etc. Generally, two synthetic methods have previously been used to prepare the hybrid materials containing metal elements and polysiloxanes. One method involves modification of prefabricated metal oxide particles with organosilanes or polysiloxanes. This particle modification method often confronts challenges on particle aggregation, dispersion, and opacity issues. Further, the inhomogeneity of the metal oxides severely limits their use for optical and electronic applications. The other method is based on sol-gel hydrolysis and condensation chemistries involving a two-component system of metal alkoxides and alkoxysilanes. The type of metal elements incorporated into the polysiloxane resins by this method is limited by the availability of the metal alkoxide precursors since metal elements other than Ti, Zr, Al, Ge, and Sn are either not available or difficult to synthesize.
The inventors have unexpectedly discovered that adding both a metal alkoxide and a hydrolyzable metal salt in a siloxane polymerization reaction provides a convenient method of incorporating various metal elements into an organosiloxane via Metal-O—Si and Metal-O-Metal oxo-linkages. Thus, the present invention relates to methods of making polyheterosiloxanes having at least two non-Si metal elements which utilize both metal salts and metal alkoxides.